288 THE OBSERVATORY OF ST. MARTIN, ISLE JESUS, C. E. 



pin passing in a slit, which is a very easy method of fixing it. This 

 lantern is placed on top of a copper rod of f inch thick and 4 feet 

 long : the bottom of the lantern having a piece of copper tube fixed 

 to it, a very little larger than the rod, and is thus easily removed and 

 replaced. To the lower end of the copper rod is soldered an inverted 

 copper funnel, a paraphiie, for protecting the glass insulating pillar 

 upon which it is fixed by means of a short tube firmly soldered to the 

 underside of the parapluie. This glass pillar passes into and is fixed 

 firmly in a wooden box, and is freely exposed to the heat of a second 

 lamp, which is placed in this box. It is trimmed at the same time as 

 that in the collecting lantern, aud keeps warm and dry the glass pillar, 

 by that means securing a more perfect insulation. !From this 

 upright rod and collecting apparatus descends a thick copper wire 

 which serves to convey the accumulated electricity to the receiver 

 which is placed in the observatory. 



The receiver consists of a cross of brass tubes (gas tubes), each 

 about 2 feet long, and is screwed into a large tube fitting upon a 

 glass cone, which is hollow, forming a system of hollow pipes for the 

 passage of the heat internally, and keeping up a certain amountof dry- 

 ness and consequent insulation. The glass cone is fixed upon a table 

 over an opening made in it, fitting to the hollow part of the cone. 

 Immediately under this table is placed a small stove of sheet-iron, 

 about 8 inches in diameter, made double, the space of about 1 inch 

 being left between the two chambers; and this plan has beea 

 found to effect a good insulation by keeping the whole of the appa- 

 ratus warm and dry. Charcoal is used as fuel, and is, I think, prefer- 

 able to a lamp. A coating of suet or tallow is applied to the glass 

 cones or pillars. Care must betaken not to rub or polish the collect- 

 ing apparatus as it seems to deteriorate its power of collecting and 

 retaining atmospheric electricity ; and I have found that its collecting 

 powers increase with its age. Suspended from these cross arms hang 

 the electrometers. 1. Bennet's electroscope of gold leaves ; this scarcely 

 needs a description. 2. Volta's electrometer, No. 1, consisting of 

 two straws, two [French inches long : a very fine copper wire passes 

 through these straws, which are suspended from the cross-arms. 

 This electrometer is furnished with an ivory scale, the old French 

 inch being divided into twenty-four parts, each being 1° ; this forms 

 the standard scale for the amount of tension. 2. Volta's electrO' 

 meter, No. 2, is similar to the JSTo. 1, but the straws are five times 

 the weight of No. 1, so that one degree of Volta's No. 2 is equal to 



